Scientists Breed Exercise-Crazy Rats

Thirty-six genes may hold the secret for why some rats preferred running on wheels ten times as much as other rats

Some rats may be genetically predisposed to being more or less inclined to exercise, new research from the University of Missouri shows. In the study, scientists selectively bred rats that were either exercise maniacs or extremely averse to doing any physical activity whatsoever.

The team kept rats in cages containing running wheels. Over six days, the researchers observed which rats were natural gym rats, willingly running on their wheels, and which were not. From these observations, they bred the 26 most athletically inclined rats with one another and did the same with the 26 rats that were least inclined to run. They repeated these steps through ten rat generations. In the end, the exercise-prone rats ran ten times more than the “lazy” rats, they describe.

From these specially bred lines, they examined the rats’ levels of mitochondria—the so-called powerhouse organelles—within muscle cells and undertook genetic sequencing of each rat’s RNA. They also studied the rats’ body composition. Levels of physical fitness or numbers of muscle mitochondria, they found, didn’t differ much between the two rat groups. Genetics, on the other hand, did differ. From more than 17,000 genes occurring in one part of the rats’ brains, they found, 36 differed between the two groups and could potentially play a role in whether or not the animals preferred exercising or lounging around.

While a wide biological gap exists between humans and rats, the researchers do propose that some people could be genetically predisposed against exercising. Although a few recent studies have shown that problems like childhood obesity may have less to do with inactivity than with environmental factors like unhealthy eating and lack of sleep, this hypothesis could be worth investigating in the context of the 97 percent of American adults who engage in fewer than 30 minutes of exercise per day.

“It would be very useful to know if a person is genetically predisposed to having a lack of motivation to exercise, because that could potentially make them more likely to grow obese,” the researchers write.

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